Among the numerous types of engineered containers manufactured to a high degree of precision common in modern industry, are, for example, toner cartridges for laser printing. In the case of toner cartridges, a high degree of precision in manufacture is necessary for proper operation and good printed image quality. Toner or process cartridges manufactured by original equipment manufacturers typically have new components including the wiper blade and/or doctor blade, depending upon the type of process employed. Similarly, remanufactured toner cartridges typically have aftermarket wiper blades and/or doctor blades.
In a so called laser printing device, laser light “paints” a latent image on a charged rotating photoconductive drum by altering the charge distribution on the surface of the photoconductive drum such that the photoconductive drum attracts charged toner particles to only that portion of its surface having the latent image. The charged toner particles are subsequently transferred from the charged rotating photoconductive drum to a medium such as paper. Thereafter, as the photoconductive drum continues to rotate, any residual toner particles remaining on the photoconductive drum are removed by a wiper blade to assure that the photoconductive drum surface is clean for receipt of the next image. The wiper blade typically has a flexible polymeric working surface that contacts the surface of the rotating photoconductive drum. In the course of the working life of the cartridge, before the supply of toner is exhausted, the surface of the wiper blade in contact with the rotating photoconductive drum wears or erodes reducing the efficiency of the wiper blade to remove residual toner. This wear or erosion of the working surface of the wiper blade eventually will permit residual toner particles to remain on the photoconductive drum through the next image “painting” cycle thus degrading the quality of the next printed image. Heretofore, it has been necessary for a remanufacturer to replace the wiper blade to achieve good printed image quality over the work cycle (i.e., consumption of the entire toner supply of the cartridge) of a remanufactured toner cartridge.
In addition to the wiper blade, toner cartridges typically also include a component referred to in the art as a doctor blade. The doctor blade has a dual propose. First, it serves to meter a uniformly thin layer of toner particles on the surface of a rotating developer roller that has acquired a deposit of toner on its surface. Second, the doctor blade functions to help uniformly charge the toner deposited on the surface of the developer roller. After passing the doctor blade, a portion of the toner on the developer roller is in turn transferred to the surface of the photoconductive drum carrying the latent image to be printed.
In laser printers designed for non-magnetic toners, the doctor blade is electrically charged and in direct contact with the surface of the electrically charged rotating developer roller. In this type of printer, the doctor blade is typically made of a relatively rigid and noncompliant material such as steel. Also, compliant doctor blades having relative stiffness along the direction of the circumference of the developer roller and relative flexibility along the direction of the axis of the developer roller are known, as described in U.S. Pat. No. 5,702,812 to Bracken, et al. The interaction of the charged doctor blade and charged developer roller together with the mechanical forces on the toner particles at the point of contact between the blade and roller results in a uniform thin layer of charged toner particles passing under the doctor blade on the surface of the developer roller.
Central to proper operation of a doctor blade are its surface roughness and wear resistance where it contacts the developer roller. The surface roughness of the doctor blade is a design parameter in the construction of the component. Too smooth a surface where the doctor blade contacts the developer roller allows excessive toner to be metered under the blade. On the other hand, too rough a surface allows too little toner under the blade. In either circumstance, the printed image quality is degraded by such variations in the toner layer.
In laser printers designed for magnetic toners, the doctor blade is typically fabricated with a portion having a working surface composed of a compliant material, such as an elastic polymer. In this type of printer, the electrically negatively charged doctor blade is in direct contact with the surface of a negatively electrically charged rotating magnetic roller to which a deposit of magnetic toner has become attached. As the magnetic roller continues to rotate, the deposited toner accumulates behind the doctor blade. The mechanical interaction between the toner particles results in a negative electrostatic charge accumulation on the toner particles. This results in a uniform thin layer of charged toner particles passing under the doctor blade on the surface of the magnetic roller. After passing the doctor blade, a portion of the toner on the magnetic roller is in turn transferred to the positively charged regions of the surface of the photoconductive drum carrying the latent image to be printed.
The effective life of a doctor blade in a toner cartridge intended for use with non-magnetic toner is limited by the wearing away of its surface roughness where it contacts the developer roller. In the course of a working cycle of a toner cartridge the engineered roughness of the contacting surface is often worn to a degree that its continued use would result in degradation of printed image quality. Similarly, the effective life of a doctor blade in a toner cartridge intended for use with magnetic toner is limited by the erosion of its elastomeric surface where it contacts the magnetic roller. In the course of a working cycle of a toner cartridge the elastomeric surface contacting the magnetic roller is often eroded to a degree that its continued use would result in degradation of printed image quality by allowing excess toner to pass the doctor blade. Thus, it is common practice for a toner cartridge remanufacturer to replace the used doctor blade with an original equipment or aftermarket component. Moreover, a doctor blade, being precision engineered, is a relatively expensive component. Therefore, toner cartridge remanufacturers would find it is desirable to extend the effective life of the doctor blade to more than one working cycle of the toner cartridge.